Every good web designer or developer knows that JavaScript is one of the big three of web languages, along with (X)HMTL and CSS.

JavaScript adds interactivity that can make any website more engaging, and, for ecommerce websites, more engaging can often mean more profitable. And thanks to the popularity of JavaScript libraries (and frameworks), which provide various JavaScript controls and functions that make development much faster, you can add interactivity to your site in very short order.

To make it even easier to interject JavaScript-driven interactivity into your next site project, I’ve enumerated many of the available JavaScript libraries. Some are going to be familiar like jQuery or Prototype, while others might represent new opportunities to easily add functionality.

Prototype JavaScript Framework

Prototype is the JavaScript framework employed in the popular Magento Commerce platform. And while it is certainly possible to use other JavaScript libraries with Magento, you can avoid some potential conflicts by employing Prototype when you’re building on Magento.

Script.aculo.us

An extension of Prototype, Script.aculo.us offers a number of excellent effects and is very easy to use. Be sure to check out the drag and shop demonstration.

jQuery and jQuery UI

“Designed to change the way that you write JavaScript,” John Resig’sjQuery and its offspring jQuery UI has rapidly become, perhaps, the most popular JavaScript framework. It is known for being lightweight, concise, and powerful—things that make most designers happy.

Moo Tools Compact JavaScript Framework

The well-written Moo Tools library makes the standards-crazed developers smile in joy. The framework is essentially error free. What’s more, the code has an Italian flair that reminds me of home cooking.

Dojo, The JavaScript Toolkit

“Dojo is an open source DHTML toolkit written in JavaScript. It builds on several contributed code bases (nWidgets, Burstlib, f(m)), which is why we refer to it sometimes as a ‘unified’ toolkit,” according to the Dojo Website. “Dojo aims to solve some long-standing historical problems with DHTML that prevented mass adoption of dynamic web application development.”

Ext JS

Ext JS is a professional-grade JavaScript framework that offers both commercial and GNU GPL Licenses. The framework includes a lot of user interface controls and there are dozens of samples available. The framework also works well with others—even other languages like Flash.

YUI

Yahoo! User Interface Library (YUI) is a comprehensive and powerful JavaScript and CSS framework that provides many widget, plug-ins, and resources that will make creating your next website faster and easier. It is also worth mentioning that this is the framework that powers the Yahoo! homepage.

MochiKit

Created by Bob Ippolito to help make JavaScript “suck less,” MochiKit is a lightweight JavaScript library that has an interactive interpreter so you can text your code without writing a HTML. You can also check out MochiKit’s JavaScript Regular Expression Explorer.

The Closure Library

Earlier this month, Google Labs released its Closure Library for JavaScript. The Library seems to draw from other JavaScript frameworks, and, according to Google is “broad, well-tested, modular, and cross-browser compatible.

Spry

Adobe’s Spry framework is an easy-to-use library that will have you pumping out AJAX-powered pages in no time. And Spry can be used with server-side technologies, too. Finally, it is compatible with Adobe AIR.

SmartClient AJAX RIA System

SmartClient aims to be a “comprehensive approach to enterprise AJAX” and includes a number of impressive examples.

Rico

Providing “responsive animation for smooth effects and transitions,” Rico, which is sometimes called OpenRico, is proven JavaScript Library.

UIZE JavaScript Library

The UIZE JavaScript Library, which is oddly pronounced, “you eyes” provides a framework for using JavaScript for AJAX, RIA, widgets, JSON, OOP and others.

Echo Web Framework

With the Echo Web Framework is great for asynchronous JavaScript and XML (AJAX) or you can create applications in server-side Java code. You get to pick.

OpenLink AJAX Toolkit

The OpenLink AJAX Toolkit offers a variety of complete widgets, including a complete widget for producing pivot tables.

Qooxdoo

In spite of being hard to spell and pronounce, Qooxdoo enables developers to create some impressive web applications.

RIALTO

The Rich Internet Application Toolkit or RIALTO, is an AJAX-based widget library that “can be encapsulated in JSP, JSF,.Net, Python, or PHP graphic components.”

Raphaël JavaScript Library

The Raphaël JavaScript Library aims to simplify vector graphics. The library uses the World Wide Web Consortium (W3C) scalable vector graphic (SVG) recommendation and vector markup language in conjunction with JavaScript event handlers to create some nice graphic interactivity.

jsAnim

jsAnim is Kevin Dolan’s JavaScript animation library that creates visual effects that can rival some Adobe Flash animations.

jsDraw2D

If you want to give users the ability to draw graphs or if you need to add graphics to drawing functions, you’ll want to consider the jsDraw2D Graphics Library for JavaScript.

Editor’s Note: Did we miss a library you use? Please tell us about it in the comments.